The immediate early gene early growth response 3 (EGR3) is associated with schizophrenia and expressed at reduced levels in postmortem patients' brains. We have previously reported that Egr3-deficient (-/-) mice display numerous schizophrenia-like behavioral abnormalities. Moreover, their reduced sensitivity to the sedating effects of clozapine, compared with wildtype (WT) littermates, parallels the unexplained clinical observation that schizophrenia patients display a markedly heightened tolerance to antipsychotic side effects compared to healthy controls. Our preliminary studies reveal that a nearly 70% loss serotonin 2A receptor (5HT2AR) binding in the prefrontal cortex (PFC) of Egr3-/- mice appears to be the mechanism underlying this effect. Since schizophrenia patients also show a decreased expression of cortical 5HT2ARs, this suggests that regulation of 5HT2ARs may be a mechanism through which Egr3 influences schizophrenia risk. The goal of the current proposal is to fully characterize the anatomic localization and molecular mechanism of 5HT2AR regulation by Egr3, and to establish which of the Egr3-/- schizophrenia-like behavioral abnormalities are mediated by 5HT2AR deficiency. In Aim 1 we will use immunohistochemistry and in situ hybridization to anatomically define 5HT2AR expression in Egr3-/- mice. In Aim 2 we will use quantitative RT-PCR to determine the ability of environmental stress to modulate the regulation of Htr2a by Egr3. We will conduct chromatin immunoprecipitation and luciferase reporter assays to test the hypothesis that Egr3 regulates Htr2a expression through promoter binding. Aim 3 proposes to use virus-mediated overexpression of 5HT2AR to rescue the schizophrenia-like phenotypes of Egr3-/- mice, testing the hypothesis that the 5HT2AR-deficiency mediates these abnormalities. Identification of mechanisms by which Egr3 regulates another schizophrenia susceptibility gene will enhance our understanding of how numerous candidate genes may act in a biological pathway to influence risk for schizophrenia. Verification of such a pathway should elucidate targets for development of novel treatments for this devastating disorder.